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/*!
\file vector/neta/articulation_point.c
\brief Network Analysis library - connected components
Computes strongly and weakly connected components.
(C) 2009-2010 by Daniel Bundala, and the GRASS Development Team
This program is free software under the GNU General Public License
(>=v2). Read the file COPYING that comes with GRASS for details.
\author Daniel Bundala (Google Summer of Code 2009)
*/
#include <stdio.h>
#include <stdlib.h>
#include <grass/gis.h>
#include <grass/Vect.h>
#include <grass/glocale.h>
#include <grass/dgl/graph.h>
/*!
\brief Get number of articulation points in the graph
\param graph input graph
\param[out] articulation_list list of articulation points
\return number of points
\return -1 on error
*/
int NetA_articulation_points(dglGraph_s * graph,
struct ilist *articulation_list)
{
int nnodes;
int points = 0;
dglEdgesetTraverser_s *current; /*edge to be processed when the node is visited */
int *tin, *min_tin; /*time in, and smallest tin over all successors. 0 if not yet visited */
dglInt32_t **parent; /*parents of the nodes */
dglInt32_t **stack; /*stack of nodes */
dglInt32_t **current_edge; /*current edge for each node */
int *mark; /*marked articulation points */
dglNodeTraverser_s nt;
dglInt32_t *current_node;
int stack_size;
int i, time;
nnodes = dglGet_NodeCount(graph);
current =
(dglEdgesetTraverser_s *) G_calloc(nnodes + 1,
sizeof(dglEdgesetTraverser_s));
tin = (int *)G_calloc(nnodes + 1, sizeof(int));
min_tin = (int *)G_calloc(nnodes + 1, sizeof(int));
parent = (dglInt32_t **) G_calloc(nnodes + 1, sizeof(dglInt32_t *));
stack = (dglInt32_t **) G_calloc(nnodes + 1, sizeof(dglInt32_t *));
current_edge = (dglInt32_t **) G_calloc(nnodes + 1, sizeof(dglInt32_t *));
mark = (int *)G_calloc(nnodes + 1, sizeof(int));
if (!tin || !min_tin || !parent || !stack || !current || !mark) {
G_fatal_error(_("Out of memory"));
return -1;
}
for (i = 1; i <= nnodes; i++) {
dglEdgeset_T_Initialize(¤t[i], graph,
dglNodeGet_OutEdgeset(graph,
dglGetNode(graph, i)));
current_edge[i] = dglEdgeset_T_First(¤t[i]);
tin[i] = mark[i] = 0;
}
dglNode_T_Initialize(&nt, graph);
time = 0;
for (current_node = dglNode_T_First(&nt); current_node;
current_node = dglNode_T_Next(&nt)) {
dglInt32_t current_id = dglNodeGet_Id(graph, current_node);
if (tin[current_id] == 0) {
int children = 0; /*number of subtrees rooted at the root/current_node */
stack[0] = current_node;
stack_size = 1;
parent[current_id] = NULL;
while (stack_size) {
dglInt32_t *node = stack[stack_size - 1];
dglInt32_t node_id = dglNodeGet_Id(graph, node);
if (tin[node_id] == 0) /*vertex visited for the first time */
min_tin[node_id] = tin[node_id] = ++time;
else { /*return from the recursion */
dglInt32_t to = dglNodeGet_Id(graph,
dglEdgeGet_Tail(graph,
current_edge
[node_id]));
if (min_tin[to] >= tin[node_id]) /*no path from the subtree above the current node */
mark[node_id] = 1; /*so the current node must be an articulation point */
if (min_tin[to] < min_tin[node_id])
min_tin[node_id] = min_tin[to];
current_edge[node_id] = dglEdgeset_T_Next(¤t[node_id]); /*proceed to the next edge */
}
for (; current_edge[node_id]; current_edge[node_id] = dglEdgeset_T_Next(¤t[node_id])) { /* try next edges */
dglInt32_t *to =
dglEdgeGet_Tail(graph, current_edge[node_id]);
if (to == parent[node_id])
continue; /*skip parrent */
int to_id = dglNodeGet_Id(graph, to);
if (tin[to_id]) { /*back edge, cannot be a bridge/articualtion point */
if (tin[to_id] < min_tin[node_id])
min_tin[node_id] = tin[to_id];
}
else { /*forward edge */
if (node_id == current_id)
children++; /*if root, increase number of children */
parent[to_id] = node;
stack[stack_size++] = to;
break;
}
}
if (!current_edge[node_id])
stack_size--; /*current node completely processed */
}
if (children > 1)
mark[current_id] = 1; /*if the root has more than 1 subtrees rooted at it, then it is an
* articulation point */
}
}
for (i = 1; i <= nnodes; i++)
if (mark[i]) {
points++;
Vect_list_append(articulation_list, i);
}
dglNode_T_Release(&nt);
for (i = 1; i <= nnodes; i++)
dglEdgeset_T_Release(¤t[i]);
G_free(current);
G_free(tin);
G_free(min_tin);
G_free(parent);
G_free(stack);
G_free(current_edge);
return points;
}
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